How Does Lactic Acid Affect Muscles?

Lactic acid buildup is often blamed for post workout muscle fatigue and pain, but just how true are these claims, and how exactly does lactic acid affect muscles, fitness and performance?

First of all, let’s get familiar with the basics of the chemical process of energy production in muscle.

In aerobic metabolism, the oxygen that is required by cells to create energy is obtained via respiration. The “energy” that is produced is ATP, or adenosine triphosphate, which is a molecule that is created and stored in all body cells and provides chemical energy for cellular function. ATP provides the energy required for a muscle to contract, and is also necessary for the operation of the muscle’s calcium pump, which is involved in the sliding filament mechanism responsible for muscle contraction.

When the body is no longer able to obtain oxygen from aerobic metabolism, the energy is obtained by a process known as anaerobic cellular metabolism. Activities such as weight lifting, sprinting, or prolonged maximum output activities achieve oxygen deficit quite quickly, where more oxygen is required for cellular reactions than is available. Lactic acid is a metabolic by-product of anaerobic processes.

During anaerobic activities, energy is produced in one of two ways, the first of which involves a reaction between the creatine phosphate that is stored in muscle cells, and adenosine diphosphate (ADP). The creatine phosphate gives its phosphate molecule to adenosine disphosphate, making it “triphosphate”; therefore, the by-products of this reaction are creatine and ATP. The energy produced from this reaction is enough to last about 15 to 20 seconds, or a 100 metre sprint, then it needs to be replenished.

The second process by which anaerobic metabolism occurs is known as glycolysis – the breakdown of glycogen, which is stored energy in muscle. (glycol = sugar or glucose; lysis = splitting). ATP is a by-product of glycolysis, as is pyruvic acid. If there is still not enough available oxygen to produce more ATP in conjunction with pyruvic acid, then the pyruvic acid is converted to lactic acid and is released into the blood stream.

And this is how it happens…

Maximum contraction of a muscle during quick bursts of power, or maximal sustained effort, increases lactic acid production in muscle because blood vessels are compressed and oxygen can’t be delivered to the cells – the aerobic, energy producing pathway is insufficient to allow oxygen to fuel the reaction. As a result, an anaerobic energy production is used, and ATP and pyruvic acid are produced. The pyruvic acid is then converted to lactic acid – therefore, during an oxygen deficit, lactic acid will be the primary by-product of glucose metabolism within a cell.

When lactic acid is released from the muscle cells into the bloodstream, it is taken to the liver usually within 30 minutes of cessation of activity. In the liver it is reconverted to pyruvic acid and released into the bloodstream for further use by muscles, or it is converted to glycogen or carbon dioxide via aerobic metabolism. It is important to note at this point that lactic acid is not necessarily the “bad guy” it has been made out to be, as it still plays an important role in energy production when sufficient oxygen becomes available again.

When large amounts of glucose are used in sustained anaerobic activity, lactic acid accumulates and is alleged to contribute to muscle soreness. The buildup of lactic acid increases muscle cell acidity (hence the burning feeling in muscle) and makes ATP production more difficult. ATP is also required for the sodium-potassium pump which maintains cellular homeostasis. In the absence of ATP, the sodium-potassium pump is unable to correct any ionic (sodium, potassium etc) imbalances in the cell environment, and muscle becomes unresponsive to stimuli.

And don’t forget that the calcium pump, used in muscle contraction, requires ATP to operate. When a deficit of ATP occurs, the muscle fibres are unable to release the “cross bridges” which are created during contraction.

As a result, in either one of the two above case scenarios, the muscle may not be able to relax, resulting in cramping and spasm.

How Can Massage Therapy Assist with Lactic Acid removal?

Ok, so maybe you don’t really care about how this all transpires, and that’s fine. Here is what you need to know about lactic acid if you are a fitness enthusiast:

The claim that lactic acid causes muscle pain has been disproven, as mentioned in the article Lactic Acid Does More Than Cause Fatigue , though it is known to cause fatigue. If this is the case, then my (educated) guess is that muscle pain is caused by micro-tearing and inflammation of muscle fibres due to over-exertion.

There is also some debate concerning the degree of assistance that massage therapy can lend to the removal of lactic acid from muscle. However, as mentioned in my previous article, Massage Therapy, Fitness and Optimal Performance , massage therapy has both a mechanical and chemical effect on the body, and I believe for these reasons, it can have a positive influence on the removal of lactic acid from muscle tissue.

Mechanically, the stretching, manipulation and kneading of tissue will assist in “unhooking” the cross bridge created during contraction and relieve some cramping and spasm. Increasing circulation by this mechanical effect will assist in oxygen delivery and waste removal to and from muscle respectively. In addition, the chemical effects of massage, causing increased blood vessel permeability, will also assist in the process. And, also, don’t forget about the release of endorphins as a benefit of massage, which can help alleviate pain.

To learn more about the physiology behind this topic, please refer to my source noted below:

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